The present invention relates to a motor-driven tensioning and winding device for lashing straps.
Such devices have been known for a long time, for example, as tensioning winches and ratchet spanners for tying down loads when movable goods are transported. It is also known to obtain a sufficiently secure tie-down of the load by charging or pre-loading the lashing strap with the highest possible lashing tension. If the term lashing strap is employed in this connection, this refers to a specially preferred embodiment of a lashing means in textile form. However, other lashing means, such as chains, ropes, cables and the like made of a variety of materials are also suitable for tying down loads. The conventional tensioning and winding devices produce the required lashing tension either manually or by motor, with the lashing strap always being charged with different, undefined lashing tensions. For the secure transport of lashed goods, however, a defined lashing tension is required which can be precisely determined from the weight of the load, the lashing angles, the consistency of the base of the load-carrying surface, particularly the friction effective between the load and the load-carrying surface, and the acceleration forces expected to occur during transport. Therefore, lashing tension measuring aids are known that are integrated in the tensioned strap to indicate to the operator the lashing tension exhibited in the tensioned strap during the tensioning process.
The drawback of such lashing tension measuring aids is that a drop in tension occurring during transport, for example due to settling of the load, generally remains unnoticed by the operator. If the lashing tension drops in this way to below a minimum value required to secure the load, parts of the load or, in the worst case, the entire load may drop from the load-carrying surface.
In order to prevent a drop in the effective lashing tension to below the critical minimum value, a tensioning winch is known which is driven by a compressed-air motor and can be mounted on or at the load-carrying surface of a truck and which is equipped with a control valve that charges the compressed-air motor with a desired pressure. This desired pressure can be set manually at the control valve. The compressed-air motor itself drives, by way of a drive assembly, a wind-up spindle for the lashing strap, thus winding the lashing strap around the rotating wind-up spindle. In this way, the tensioned strap is charged with an increasing lashing tension. A possible drop of the lashing tension effective in the tensioned strap is connected with a simultaneous drop in the actual pressure in the system. The compressed-air motor continues to rotate the wind-up spindle in the winding direction and the lashing strap continues to be wound up until the desired pressure set at the control valve is reached again. The particular drawback here is the exclusive control of the tensioning force by way of the desired pressure set at the control valve since this desired pressure is a function of the torque exerted by the tensioned strap on the wind-up spindle and on the drive assembly, respectively. However, the torque acting on the wind-up spindle is decisively influenced by the diameter of the strap coil on the wind-up spindle. This inevitably results in the drawback that, due to the increasingly larger coil diameter, the desired, defined lashing tension is no longer reached if re-tightening is effected by means of the originally set desired pressure. Consequently, the return signal in the form of the torque acting on the wind-up spindle for the described control circuit in the prior art tensioning winch is being measured only indirectly.